Major reorganization of header files. Headers now have the names
described in the draft C++ standard. (Old header names are
provided as well for backward compatibility.) The new-style
headers declare their contents in namespace std; the
old-style headers do too, but they import those declarations into
the global namespace with using declarations. So, for example,
#include <vector.h> is roughly equivalent to
#include <vector> followed by the declaration
using std::vector;.
Note that namespace std is only enabled for compilers
whose support for namespaces is sufficient; this is controlled by
the header <stl_config.h>.